The present invention relates to the field of sealing systems, particularly internal seal systems for coaxial cables. The preferred seal systems are particularly well suited for use in difficult environments wherein it is desirable to seal inside a coaxial cable without the normal means available such as o-rings in machined grooves, metal o-rings, or a split metallic ring. One such application is in data transmission systems for downhole environments, such as along a drill string used in oil and gas exploration or along the casings and other equipment used in oil and gas production.
The goal of accessing data from a drill string has been expressed for more than half a century. As exploration and drilling technology has improved, this goal has become more important in the industry for successful oil, gas, and geothermal well exploration and production. For example, to take advantage of the several advances in the design of various tools and techniques for oil and gas exploration, it would be beneficial to have real time data such as temperature, pressure, inclination, salinity, etc. Several attempts have been made to devise a successful system for accessing such drill string data. One such system is disclosed in co-pending U.S. application Ser. No. 09/909,469 (also published as PCT Application WO 02/06716) which is assigned to the same assignee as the present invention. The disclosure of this U.S. application Ser. No. 09/909,469 is incorporated herein by reference. Another such system is disclosed in co-pending U.S. application Ser. No. 10/358,099 the title of which is DATA TRANSMISSON SYSTEM FOR A DOWNHOLE COMPONENT file on Feb. 3, 2003. The disclosure of this U.S. application Ser. No. 10/358,099 is herein incorporated by reference.
Downhole data transmission systems use seals to protect the electrical transmission line from the drilling environment such as the system described above. Drilling fluids such as drilling mud are pumped down the center of a drilling tool for many purposes such as to flush out cuttings on the bottom of the borehole. Drilling fluids are often corrosive which increases the difficulty of making a successful seal. A borehole created by drilling can have various temperature and pressure ranges as the depth of the borehole increases. Due to the large range and subsequent combinations of temperatures and pressures along the depth of the borehole, a robust seal design is necessary to protect the electrical transmission line of a data transmission system.
Briefly stated, the invention is a sealing system used to seal within an electrical transmission line particularly a coaxial cable. Another aspect of the invention is a system for sealing an electrical transmission line within a string of downhole components.
In accordance with one aspect of the invention, the system includes a plurality of downhole components, such as sections of pipe in a drill string. Each component has a first and second end, with a first communication element located at the first end and a second communication element located at the second end. Each communication element includes a first contact and a second contact. The system also includes a coaxial cable running between the first and second communication elements, the coaxial cable having a conductive tube and a conductive core within it. The system also includes a first and second connector for connecting the first and second communication elements respectively to the coaxial cable. Each connector includes a conductive sleeve, lying concentrically within the conductive tube, which fits around and makes electrical contact with the conductive core. The conductive sleeve is electrically isolated from the conductive tube. The conductive sleeve of the first connector is in electrical contact with the first contact of the first communication element, the conductive sleeve of the second connector is in electrical contact with the first contact of the second communication element, and the conductive tube is in electrical contact with both the second contact of the first communication element and the second contact of the second communication element.
In accordance with another aspect of the invention, the drill components are sections of drill pipe, each having a central bore, and the first and second communication elements are located in a first and second recess respectively at each end of the drill pipe. The system further includes a first passage passing between the first recess and the central bore and a second passage passing between the second recess and the central bore. The first and second connectors are located in the first and second passages respectively. Preferably, each section of drill pipe has a portion with an increased wall thickness at both the box end and the pin end with a resultant smaller diameter of the central bore at the box end and pin end, and the first and second passages run through the portions with an increased wall thickness and generally parallel to the longitudinal axis of the drill pipe. The box end and pin end is also sometimes referred to as the box end tool joint and pin end tool joint.
In accordance with another aspect of the invention, the components are sections of drill pipe, drill collars, jars, and similar components that would be typically found in a drill string.
In accordance with another aspect of the invention, the system includes a coaxial cable with a conductive tube and core within it, a base component that is placed within the conductive tube, a washer, and a seal stack placed on top of the washer. The seal stack is formed from a combination of an elastomeric component and a flexible rigid component, a detailed description of which will be found below. Each of these components is placed within the conductive tube with the elastomeric component of the seal stack in a compressive state. The contact extending from the communications element goes through the center portion of these components thus forming a seal between the contact and the internal diameter of the conductive tube.
In accordance with another aspect of the invention, the method includes placing a seal within a coaxial cable with an electrical lead passing through the seal.
In accordance with another aspect of the invention, the method includes placing a base component inside the conductive tube of the coaxial cable. The base component includes a means to mechanically engage the internal diameter of the conductive tube thus holding the base component in place. The method also includes a washer and seal stack are then placed inside the conductive tube with the washer lying on top of the base component and the seal stack on top of the washer. The method further includes a contact, which is pushed through the central portion of the seal stack, the washer, and the base component to an electrical connector placed beyond the base component thus making electrical communication with the coaxial cable. If necessary the contact passes through a tubular spacer which then forces the seal stack within the conductive tube as the contact is pushed through each of the components.
The present invention, together with attendant objects and advantages, will be best understood with reference to the detailed description below in connection with the attached drawings.